1. Field of the Invention
The present invention relates to an optical network technologies, and particularly to a monitoring apparatus and a monitoring method for an optical network.
2. Description of Related Art
As science and technologies developing rapidly, network technology is developed for long distance information transmitting/receiving. Networks have now been important tools for information communication. Among many kinds of networks, optical network is extremely highlighted since it can transmit large amount of information and occupies small space. However, the medium for constructing an optical network, optical fibers are mechanically weak and easy to be broken. Therefore, fiber-faults such as broken points or other quality defects in an optical fiber are usually need to be monitored.
Conventional methods for monitoring broken points include two typical ways. One is using an optical time domain reflectometer (OTDR) for monitoring the optical network. The other is employing a combination of an optical fiber amplifier and a fiber Bragg grating (FBG). FIG. 1 is a schematic structural view for illustrating the OTDR method. Referring to FIG. 1, an optical network 100 includes a plurality of fiber channels or fiber branches, for example 5 fiber channels herein. The fiber channels are all coupled to an optical splitter 102. The optical splitter 102 is adapted for splitting optical signals inputted from the OTDR 104 into the fiber channels. A monitoring unit 106 is coupled to the optical splitter 102 for monitoring levels of the optical signals. FIG. 2 is a schematic diagram for illustrating levels of signals monitored by the monitoring unit 106 of FIG. 1. When the fiber channels are operating properly, the levels of the optical signals are sustained at a higher level 110. When for example there is a broken point 108 in a fiber channel 1, a lower level of optical signals can be detected. The OTDR method has an advantage of being capable of knowing the position of the broken point 108. However, under an entire network structure, which fiber is broken can not be identified. Although some prior arts also propose to use a plurality of OTDR for one to one monitoring the fiber channels, it is incredibly expansive and uneasy to perform.
Referring to FIG. 3, it illustrates a conventional optical fiber amplifier method. According to this method, each fiber channel has a fiber Bragg grating (FBG) 101 disposed thereby, each of the FBG having a specific central wavelength. To monitor each of the fiber channels, an optical fiber amplifier 112 generates an optical signal, and a fiber loop type laser unit 114, e.g., erbium-doped fiber amplifier (EDFA), further amplifies the optical signal for checking each fiber channel. The method using optical amplifier is not convenient to operate, and the optical amplifier is relatively expansive. Particularly, an optical fiber amplifier can support limited optical fibers under such a conventional network structure. If many optical fiber amplifiers are used, it will be more expansive. Therefore, the optical fiber amplifier method is not an ideal way either.
Therefore, a fiber-fault monitoring apparatus and a monitoring method having better monitoring efficiency and lower cost are highly demanded.